Fitting rabbit..any clues anyone??

Up until last night, I had a 5 year old, felmale dwarf lop rabbit. SHe's alwyas lived indoors, always had the option to roam freely, but has chosen not to for the past 3 years, choosing to spend all her time in an open cage   She's always been healthy, grumpy but very healthy, claws clipped, loved a head and ear stroke, no issues with her at all.
Tea time yesterday she was fine, 11pm, she's gone off her back legs but kept jumping round the cage and falling over. By 1pm she was having full blown....fits, I presume, arching her back so that her head touched her bum, rigid limbs, eyes vacant, and panting. She'd relax for a few seconds, but still shallow panting, and then do it again. Everynow and then she'd thrash wildly around the cage and start the arching thing again. AFter 3 hours of this, and her breathing becoming more laboured, my OH decided to do the kind thing. There were no vets open within reachable distance, the one we phoned said it probably was neurological and that she's be gone by the morning anyway. Awful night.
Anyone had anything similar or have any idea what it could be?? I'm just amazed at how quickly it came on and how fast she deteriorated.

Poor you - that sounds horrible    You did the best thing you could have done and ended her suffering. 

She could  have been dehydrated or running a temperature due to some underlying illness and that could have set off the fits, but that's typical of animals.  Don't show illness until it gets really serious and then it's too late to help